The present invention relates to the manufacture of paperboard boxes and, more particularly, an improved method of dispersing adhesives between two opposing surfaces of paperboard material for securely bonding them together, for example, for manufacturing corrugated cardboard and adhering together sections of corrugated cardboard.
A wide variety of machinery is employed in assembling and sealing a very great variety of designs of containers or boxes made of paperboard or corrugated cardboard material. The box designs commonly require that different panels of a single blank of material or that a pair of complementary panels of a plurality of blanks be glued together in laminated relationship. A common method of dispersing adhesive between two such opposing surfaces is to apply mechanical pressure external to the bonding surfaces. The means of applying mechanical pressure may be opposing rollers, traveling belts, pressure plates, wedging a material between two pressure members or other similar mechanical arrangements.
The application of pressure effects the dispersal of the adhesive for bonding the pair of panels together but, particularly in the case of corrugated board panels, the structure of the board limits how much pressure can be applied. Corrugated board is well known for its strength under a load applied to the flute ends, as in an edge crush test, but it is not well adapted to resist crushing under loads applied to the face of the board. Thus, the amount of pressure applied to the faces of the corrugated cardboard must be moderated to avoid damage to the cardboard. Also, as a hot melt adhesive is commonly employed in the case of corrugated board, if its heat energy is not rapidly transferred into the adjacent structures, a relatively long dwell time during which the pressure is applied is required for penetration of the fiber of the board by the adhesive so that only relatively low production rates can be achieved.
Additionally, there are also types of box designs in which it is not possible to develop adequate dispersing pressure mechanically because mechanical means can only be applied from one side of the mating components.
Corrugated cardboard consists of a fluted core of material that is sandwiched between a top and a bottom layer of linerboard. In the manufacture of corrugated cardboard, linerboard (a special type of flat cardboard sheet) is softened with steam to make it pliable. The pliable linerboard is then fed between metal rollers that have special meshed, gear-like teeth which press the board into a series of permanent wavy curves (flutes). Next, an adhesive (e.g., cornstarch or water-based resin) is applied to the tips or apices of the flutes at their tops and bottoms. Flat linerboard is applied to the fluted material and steam heated platens activate the adhesive to adhere the flat linerboard to the fluted linerboard and form the corrugated cardboard sheets. Immediately after its formation, the corrugated cardboard is moist, and must be allowed to dry out. This requires that the newly formed corrugated cardboard be held in a drying area before being used.
There accordingly remains a need for improved methods of manufacturing corrugated cardboard and also better methods for joining adjacent sections of corrugated cardboard in the assemble of corrugated cardboard containers.